Production of titanium and zirconium by the electrolytic refining of their alloys



United States Patent PRODUCTION OF TITANIUM AND ZIRCONIUM BY TH];ELECTROLYTIC REFINING OF THEIR ALLOY Emile Pruvot, Claude Boulanger, andPaul Louis Adrien Belon, Saint-Jean-de-Maurienne, France, assignors toSobertiz, Societe de Brevets dExploitations et de RecherchesMetallurgiques, Paris, France, a corporation of France No Drawing. FiledMar. 12, 1957, Ser. No. 645,399 Claims priority, application France Mar.20, 1956 6 Claims. (Cl. 204-64) It has already been proposed to refineelectrolytically highly contaminated titanium and zirconium metals whichcould not be used commercially in that condition because of theexcessive content of impurities. The metals intended to be processed inthat way generally contained oxygen and nitrogen as main impurities.These metals were used as anodes in a molten bath composed of alkalineor alkaline earth metal halides and containing a small proportion ofhalides of the metal to be purified.

The present invention, which is based on the researches of theapplicants, has for its object the direct extraction of titanium orzirconium from alloysof these metals by electrolytic refining. j

A preferred form of the invention consists in extracting titanium fromferro-titanium or ferro-silicon-titanium alloys by using these alloys asanodes in a molten bath of alkali halides containing titanium in theform of chlorides-preferably as TiCl and using a voltage not in excessof two volts. In this way,. there is obtained at the cathode a depositof titanium substantially free of iron and silicon.

The process can be carried out in the same way by starting with thecorresponding zirconium alloys.

In order to obtain a very pure metal at the cathode, it is advisable toselect for the anode an alloy which does not contain, or contains only avery small amount of metals capableof forming a solid solution with themetal to be obtained. In the case of titanium, it is advisable to avoidthe presence of aluminum and vanadium,

' It is also preferable that the anodic alloy contain but smallproportions of manganese and chromium.

The anodic alloy can be crushed into lumps of the size of walnuts orhazelnuts which are placed in a metal basket. Some titanium or zirconiumchips can also be added and, by their presence in the bath, keep thechloride of the metal to be refined in the subchloride state.

In order to obtain a selective attack on the alloy forming the anode, itis preferable to adopt a moderate anodic current density, for example,less than 100 amperesper kilogram of alloy. Since the anode isconstituted of the alloy in comminuted form placed in a basket, it ispractically impossible todeterrnine its exact surface. For this reason,the current density has been defined in terms of amperes per kilogram ofanodic alloy.

It has been established that the alloy to be refined, which is used asanode in a bath of molten metal chlorides, is not directly attacked bythe chlorine ions derived from the titanium or zirconium subchloridesdissolved in the electrolytic bath. These chlorine ions trans form thetitanium or zirconium subchloride into the tetrachloride, and it is thistetrachloride which dissolves selectively the titanium or zirconium outof the anodic alloy, while being itself converted into subchlorideswhich are soluble in the bath.

It has also been established that not all titanium or zirconium alloysare capable of being refined under actual commercial conditions, becausethe solution of the titaprocessed in the same manner.

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nium or zirconium out of the anodic alloy sometimes proceeds too slowlyor incompletely. Accordingly, a procedure which forms a part of thepresent invention consists in submitting the alloy to be refined to ablank test by reacting TiCl or ZrCl with this alloy which is placed inthe bath of molten chlorides, for example, at a temperature of 750-800C., but in the absence of any electric current. Thereupon, the bath isanalyzed to determine the proportion of titanium or zirconium subchlorides contained therein, which permits calculation of the eificiencyof the dissolution of the alloy.

Alloys having a solution efiiciency which reaches or exceeds can berefined under good conditions.

In this way, it has been established that the alloys to be refinedshould contain at least 65% and, preferably, 70% or more of titanium orzirconium.

It has likewise been established that it is preferable to use for therefining operation those titanium or zirconium alloys the oxide plusnitride content of which does not exceed 8%.

The following examples, which are not given by way of limitation, relateto alloys which fulfill the precise requirements stated above. Theseexamples describe the refining of titanium alloys. Zirconium base alloysare Example 1.Refining of Fe-Ti 1 kg. ferro-titanium alloy, containing72.5% Ti and 19.9% Fe, was crushed to walnut and hazelnutsizes andplaced in a perforated iron basket, which was then intro duced into aNaCl bath kept under an atmosphere of'a suitable inert gas. TiCl, (whichhad been partiallyfreduced-to TiCl by the ferro-titanium) was injected"into the bath. until the titanium content of the bathir'eached 3.90%.The bath thus prepared was then. submittedl to electrolysis using thebasket as the anode and, on passing current of 55 amperes at a voltageof l=to 1.5 v. ;.with a counterelectromotive force of 0.1 to 0.3, v;,therewas obtained at the cathode a crystalline titanium depositin-Altogether, 410 g. titanium were deposited.

A residue weighing 250 g. was removed from the basket; the Fe-Ti lumpshad kept their shape but had become extremely friable. They contained9.9% Ti'and 59.4% Fe. The rest of the titanium was found in the slimeson the bottom of the cell.

The titanium that had been deposited 0.025% Fe.

' Example 2.Refining of Ti-Si A titanium-silicon alloy comprising 72%Ti, l-1% Fe and 11% Si, was electrolyzed in a moltenbath containing2.75% Ti as TiCl After washing, the obtai'iiii cathodic deposit assayed0.05% Fe and 0.09% Si.

7 It was proven that the Ti content of the bath did not change duringthe electrolysis.

, When the electrolysis was stopped, it was observed that the anode wassurrounded by a porous layer and that the titanium content of the anodehad dropped-to 59.65%, while that of the Si had risen to 18.35%.

It is also possible to submit to the electrolytic refining process ofthe present invention alloys rich in titanium but containing variousadditional elements as, for example, aluminum, chromium, vanadiumor'manganese. In such cases, the content of the additional elements inthe cathodic titanium or zirconium deposit varies greatly depending onthe procedure adopted, permitting thereby considerable flexibility shownby the following examples relating to titanium alloys, which do notlimit theinyention in any way.

ce ih' "Example 3.--Refiriing f Al-Ti The-commercial Al-Ti alloy havinga 70% Ti content is used as the soluble anode in a molten bathcontaining ,about titanium in the form of subhalides. The electrolysisis effected with an interpolar distance large "enough torequire 5 v.when an 80 amperes'current is passed through the cell, the'counter-electromotive force being of the order of onlyv 0.6 v. Titaniumcrystals containing l to 5% Al are collected at the cathode.

Example 4 'TIheanodic alloy is TiCrFe containing 2.7% chromium I and1.3% iron.

The anode isconstituted of 4 kilos scrap alloy. An average current of3.0'amper'es at a voltage of the order of 1 volt is passed through amolten bath at 750 C.

At the beginning of the electrolysis, there is obtained 'at thecathodetitanium metal having a'Brinell hardness of less than 150 and containing0.07%1iron and 0.01% chromium; this resultcontinues until the depositedTi charged Ti ratio attains the value of about 27%. :If theelectrolysis'is continued without the addition ,of any fresh alloy, theiron content of the deposited titanium does not change but the chromiumcontent increases to 0.024% until the deposited Ti charged Ti ratioreaches-40%.

Beyond this point, the iron and chromium increase simultaneously. But,if fresh alloy be added at the point when,27% of the initial titaniumhas been converted 't'o refined titanium, then, titanium metalcontaining little iron and very little chromium will continue to be ob't ained at the cathode. The addition of fresh alloy can be repeated alarge number of times without altering this result.

When a slightly higher chromium content" can be tolerated in thecathodic titanium, then, fresh alloy should only be added at the timewhen the deposited Ti charged Ti ratio reaches 40% If fresh alloy is notadded, then, it is possible tosep- "arate successively difierentcathodic deposits having progressively increasing iron and chromiumcontents but which are free of oxides and nitrides, and whichcan, torexample, be remelted in the absence of air to reform an alloy of thesame composition as the initial alloy but ,of a higher quality. Theanodic residue, which is disoarded, contains under the conditionsmuchhigher proportions of iron and chromium than in the initial alloy.

3mm 22% and less than 50%, the result ng deposits are richer in Al and Vbut are free of oxides and nitrides, and when remelted in the absence ofair, they num content increases to 13-15%.

,halides. earth metals can'be used, especially those of potassium,

permit the reconstitution of Ti, 4% Al, 4% V alloy of oo .ql a ty Ofcourse, fresh alloy can be added during the refining process as has beenindicated in Example 4.

Example 6 The :anod'ic .alloy is a titanium alloy containing 4%manganese and 4% aluminum.

The electrolysis conditions are the same as in Examples -4 and S.

Manganese separates at the cathode assoon as the electrolysis begins.

'Up to a deposited Ti charged Ti ratio equal to 53% there is produced analloy at the cathode with thefollowing composition:

F6=0.02% Al=0.2% Mn=7.5 t0 3.8%

that is to say, a manganese titanium alloy containing very littlealuminum. If the electrolysis be continued :without adding fresh alloy,the manganese content of the cathodic deposit decreases to 1.52% and thealumi- How ever, if fresh alloy be added periodically before thedeposited Ti charged Ti ratio amounts to 50%, a'low aluminumtitanium-manganese alloy will continue to be produced at the cathode.

Results of the same order can be obtained when zirconium alloys are usedas the anodic alloys.

Generally stated, in the process of this invention, fresh "anodic alloyis added to the cell when .thequantity of the desired metal depositedamounts to 20-50% of the content of the desired metal in the anodicalloy.

A'molten bath of NaCl was used in-the s'everalexamples given above;however, it is to be understood that other molten halides, such asbromides, iodidesandflitorides can likewise be used; also mixtures 'ofvarious Similarly, halides of other alkaliand. alkaline strontium,calcium, barium, and'lithium. Mixtures of halidesespecially chlorides-wtseveral alkali and alkaline earth metals aresuitable for thepurposesloflthis invention. Magnesium halides can likewise be'nsedeffectively for the purposes of the present invention and in theappended claims are included in the expression halides of the alkalineearth metals.

The cathode used in thev examples was formed of iron;

,however, any other suitable material, such as .nickeLcan .be used.

We claim: :1. A process for'producing electrolytically .a desired;-metal selectedfrom the group consisting of titanium 'and zirconiumfrom alloys thereof comprising atleast one of the metals selected fromthe group consisting of .Fe, Si, Al, Cr, V and Mn, andcontainingbetween-'% and 96% of the desired metal, comprising ,the stepsof forming in an electrolytic cell, containing an anode comprising saidalloy of the desired metal and acathode, a

molten bath consisting essentially of at least-one halide of a metalselected from the :group consisting of the alkali and alkaline earthmetals; introducing into said bath a subhalide of the desired metal;passing electric current through said bath whereby the desired metal isselectively dissolved out of the anode and deposited on the cathode; andadding fresh anodic alloy'tothe cell when the quantity of the metaldeposited amounts to I20-5 0% ofthe content of the desired metal intheanodic alloy.

., '2...Pr ocess according to claim 1, whereinthernolten ,bath containsNaCl and the subhalide is the dichloride of thedesiredmetal.

3. Process according to claim 1, wherein the sum of References Cited inthe file of this patent the oxide and nitride impurities of the anodicalloy does UNITED STATES PATENTS exceed 8% by 'i 2,667,413 Jordan Jan.26, 1954 4. Process eccordmg to clalm 1 wherem the anodlc 2,734,855Schultz ct Feb. E14I 1956 a11Y 1S m- 2,817,631 Gullett Dec. 24, 1957 5.Process according to claim 1 wherein the anodrc FOREIGN PATENTS alloy isferro-silicon-titanium.

6. Process according to claim 1 wherein a minor quan- 157,894 Norway1957 tity of the desired metal is added to the bath whereby OTHERREFERENCES the presence of the subhalide of the desired metal in the 10Journal of Metals, September 1956, page '1166. bath is enhanced. Journalof Metals, September 1956, pp. 1162-1168.

1. A PROCESS FOR PRODUCING ELECTROLYTICALLY A DESIRED METAL SELECTEDFROM THE GROUP CONSISTING OF TITANIUM AND ZIRCONIUM FROM ALLOYS THEREOFCOMPRISING AT LEAST ONE OF THE METALS SELECTED FROM THE GROUP CONSISTINGOF FE, SI, AL, CR, V AND MN, AND CONTAINING BETWEEN 65% AND 96% OF THEDESIRED METAL, COMPRISING THE STEPS OF FORMING IN AN ELECTROLYTIC CELL,CONTAINING AN ANODE COMPRISING SAID ALLOY OF THE DESIRED METAL AND ACATHODE, A MOLTEN BATH CONSISTING ESSENTIALLY OF AT LEAST ONE HALIDE OFMETAL SELECTED FROM THE GROUP CONSISTING OF THE ALKALI AND ALKALINEEARTH METALS; INTRODUCING INTO SAID BATH A SUBHALIDE OF THE DESIREDMETAL; PASSING ELECTRIC CURRENT THROUGH SAID BATH WHEREBY THE DESIREDMETAL IS SELECTIVELY DISSOLVED OUT OF THE ANODE AND DEPOSITED ON THECATHODE; AND ADDING FRESH ANODIC ALLOY TO THE CELL WHEN THE QUANTITY OFTHE METAL DEPOSITED AMOUNTS TO 20-50% OF THE CONTENT OF THE DESIREDMETAL IN THE ANODIC ALLOY.